LITTLETON, Colo. — Two heavily armed students wearing trench coats and ski masks calmly walked into the cafeteria of Columbine High School on Tuesday and opened fire on terrorized schoolmates, setting off a killing spree that held police at bay for more than four hours before the gunmen apparently killed themselves.

When police SWAT teams finally entered the school, they found as many as 25 bodies, including two that authorities said appeared to be the gunmen. Another 23 students and faculty were taken to area hospitals, many in critical condition and some suffering multiple wounds.

Witnesses said the pair appeared to be stalking the school for victims, moving methodically from the lunchroom to the library as they shot victims, some of whom were cowering under desks, at close range. At least one of the gunmen appeared to be hunting for minorities and popular athletes, survivors said.

"He was shooting people right in front of me," sobbed a female student, her arms splattered with blood. "He was shooting people of color and people who play sports. He put the gun right in my face and started laughing and said it was because people were mean to him last year."

The gunmen carried guns and homemade bombs, and police late Tuesday discovered other bombs surrounding the middle-class suburban school, including two in cars in the parking lot, as well as another one in the home of one of the suspects.

"Blood was going all over," a shaken girl said as she was comforted later by her father outside the school. "They were saying that they wanted Judas for their revenge."

Jefferson County Sheriff John Stone termed the scene inside the school "gruesome" and said, "It appears to be a suicide mission." A sheriff's spokesman said the gunmen appeared to have bombs strapped to their bodies.

By late Tuesday night, officers had yet to remove any bodies from the school because of the danger of explosives and the need to preserve evidence.

FBI agents and police SWAT teams slowly made their way through the building. Some of the bodies had been set up as booby traps, said Stone.

"It's like walking through a minefield," he said.

It was the worst school shooting incident in U.S. history, far deadlier than school massacres in Oregon, Arkansas, Kentucky and Mississippi that shocked the nation in recent years.

President Clinton made a brief televised address from the White House press room Tuesday night, urging the nation to "wake up" to school violence.

"If it can happen here, then surely people will recognize that they have to be alive to the possibility that it can occur in any community in America and maybe that will help us to keep it from happening again," said Clinton, his face red and his eyes downcast.

Clinton said a team of grief counselors is being sent to Littleton.

Six months ago, Clinton hosted a White House conference on school violence and ordered Education Secretary Richard Riley and Atty. Gen. Janet Reno to develop an "early warning guide" to deal with the kind of youth rage that has led to the spate of school shootings around the country.

Clearly no one in Littleton, an affluent and fast-growing suburb a half-hour's drive southwest of Denver, spotted the danger signs in time.

Stone said both gunmen were found dead in the library of the school, which has 1,870 students. Both were masked and wore black trench coats, the trademark of a small group of anti-social Columbine students who called themselves the "Trench Coat Mafia," Stone said.

Their bodies were found shortly after they had exchanged fire with officers, police said early Wednesday.

Several students said they recognized at least one of the assailants as a member of the clique, a group of 8 to 10 teens who wore dark clothing, kept to themselves and were fans of shock rocker Marilyn Manson.

"They were known as the Trench Coat Mafia because they wore a black trench coat every day to school," said sophomore Joshua Lapp. "Everywhere, anywhere, any day, no matter how hot it was they wore a black trench coat."

Lapp said that, during Tuesday's shooting spree, the two gunmen "were going around, they were laughing about it. They'd shoot somebody, they'd laugh, they'd giggle. . . . You'd hear a shot go off, you'd hear somebody yell and scream, another shot go off and they'd yell and scream, another shot and there would be silence. . . ."

Several students and recent graduates said that social tensions between school athletes and members of the "Trench Coat" gang may have been a factor behind the attack.

"They're the kids that don't get along with the jocks," said Whitney Walker, who was standing outside the school and waiting for word about friends. "We heard their mission was to go after the jocks."